1. Field of the Invention
This invention relates to camshaft structure which translates rotary movement into reciprocal movement, and particularly concerns a cam-shaft having ceramic cam portions which have an attrition-resistant property when applied to a valve system in an internal combustion engine.
2. Description of Prior Art
In a camshaft as shown in Japanese Utility Model Provisional Publication No. 61-8171 published March 13, 1986, a ceramic cam is inserted into a metallic shaft body to improve an attrition-resistant property of the cam, and at the same time, increasing light weight property.
In this instance, a pin and a metallic sleeve are used as an axial positioning means, while a key and groove are employed to protect the cam against a rotary slip. The groove is provided in the outer surface of the metallic shaft body, and inner surface of the ceramic cam, the key is placed in both the grooves, Further, the outer surface of the shaft body and the inner surface of the cam are bonded by means of brazing.
The rotary movement of the shaft body, however, is transmitted by means of the key and grooves, so that transmission power may be locally applied at the key and grooves to establish stress concentration.
Further, it is necessary to provide the sleeve and the pin in addition to the key so as to produce a complicated structure, thus making assembling time-consuming and troublesome.
Therefore, it is an object of this invention to provide a camshaft with ceramic cam portions which is capable of obviating the stress concentration and facilitating the assembling thus leading to an improvement of production.